A number of agricultural implements need to be moved during work in a position relatively close to the ground of a field. However, in order to avoid damage, a contact between the implement and the ground needs to be avoided.
A typical example is a header for a self-propelled harvesting machine like a combine harvester or a forage harvester. Such headers include grain cutting platforms, corn pickers and corn cutting machines. In the prior art, mechanical ground height sensors have been used for an automatic header height control. These ground height sensors are pivotally mounted below the frame of the header such that they pivot around an axis extending horizontally and transversely to the forward direction and have a surface in mechanical contact with the ground. A potentiometer is coupled to the sensor and submits ground height information to a ground height controller. The latter controls an actuator for adjusting the height of the header with respect to the self propelled harvesting machine such that the height of the header above the ground corresponds to a predefined value, which is usually input by an operator. Often, at least two ground height sensors are distributed over the width of the header, in order to automatically maintain a lateral orientation of the header parallel to the ground. The ground height controller then also controls an actuator moving the header with respect to the self propelled harvesting machine around a horizontal axis extending in the forward direction. It has also been proposed to have contact-less sensors on the header that measure the distance to the ground with electromagnetic or ultrasonic waves.
One disadvantage of these sensors mounted to the header and interacting with the ground below the header, even if they are mounted at the forward end of the header, as on a divider tip (see, for example, U.S. Pat. No. 6,813,873), is that they are not able to cause a sufficiently fast lifting of the header when the header is approaching sharp rises in the ground topography. Due to the position of the sensor and the reaction time of the actuator, collisions with the ground cannot always be avoided, causing severe and expensive damage to the header. Additionally, debris such as rocks can be collected and damage parts of the header and of the harvesting machine. This problem is greater with the relatively high ground speeds of actual harvesting machines, since the required reaction time is shorter.
U.S. Pat. No. 6,615,570 discloses mounting an optical sensor to a self-propelled harvesting machine. The sensor submits electromagnetic waves towards the ground or a crop area in a distance ahead of the header and determines the flight time of the reflected waves. The elevation of the ground ahead of the harvesting machine is thus determined and used for automatically controlling the position of the header prior to the header reaching the crop area. This improves the response of the header and reduces incidences of improper header position resulting from rapidly changing contours, but requires a relatively expensive optical sensor.
U.S. Pat. No. 5,666,793 proposes driving over a field with a harvesting machine and recording the yield and the header height dependent on the position of the harvesting machine. The header height is manually selected by the operator during recording. When the harvesting machine travels over an adjacent path or (in the next harvest season) over the same path, the geo-referenced recorded header heights are used as position dependent nominal values for an automatic header height control. In this manner, the header height can be adjusted to reflect changes in the ground. Since the header height depends on manual input of the operator, at least during the first path, it is required that the latter carefully supervises the header height above the ground, especially when ground contours are rapidly changing. Further, using the header height from a previous path adjacent the actual path involves the risk of ground collisions when ground contours in the adjacent paths are significantly different.
U.S. Pat. No. 5,961,573 proposes to record the position of obstructions on a field, like rocks, by visual detection during a scouting operation or while the field is being worked or by storing information after a rock is hit by an implement such as a plow. The header of the harvesting machine is subsequently automatically lifted based upon the geo-referenced obstruction position data to avoid incidences in sufficient time before the obstruction is hit. Due to the fact that the obstruction position data is to be collected manually, this procedure is feasible only for fields with a small number of obstructions, but not for fields with rapidly changing ground contours.
U.S. Pat. No. 6,073,070 proposes to determine a terrain model of a field using sensors mounted to a header of a combine measuring the height of the header over the ground. This terrain model is subsequently used for a new treatment of the field with an available agricultural vehicle. It is not described in which manner the terrain model is used for controlling the implement position during the new treatment.
Another example of an agricultural implement with variable height adjustment is a sprayer boom. Generally, the boom is maintained by suitable actuators in a predetermined height above the ground, controlled manually or automatically based upon e.g., roughness of the ground, which is measured by detecting movement of a spring suspended front wheel frame of a tractor ( see, for example, Japanese patent JP 02 021 959 A). This detection suffers also from the disadvantage that uneven ground is detected too late to avoid ground contacts of the boom.
Thus, there is a need for a simple and reliable system for controlling the position of an agricultural implement coupled to an agricultural vehicle to control the position of the implement in a manner to avoid ground incidences at rapidly changing ground contours, independently from an operator.
It is an object of the present invention to provide a simple, reliable, and responsive system for controlling the position of an agricultural implement coupled to an agricultural vehicle.